gpio: crystalcove: Fix implicit declaration of function 'seq_printf' error

drivers/gpio/gpio-crystalcove.c: In function 'crystalcove_gpio_dbg_show':
drivers/gpio/gpio-crystalcove.c:286:3: error: implicit declaration of function 'seq_printf'
   seq_printf(s, " gpio-%-2d %s %s %s %s ctlo=%2x,%s %s %s\n",

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>